Hypodermic syringes provide an effective, reliable, and inexpensive way to inject a measured quantity of medicine below the skin. Syringes typically have exposed needles, however, and the ease by which a needle may pierce the skin creates a hazard that the healthcare worker may accidentally be stuck with a needle. The resulting injury could be as simple as a minor skin laceration, or as deadly as an infection from a virus in the patient's blood.
Because syringes are routinely used worldwide, occasional injuries are inevitable when using conventional syringes. Healthcare practitioners are exposed to this danger in routine medical practice. Diabetics, people with arthritis, and others who self-administer daily injections are at risk, as are members of their household. After disposal, conventional syringes may continue to pose a risk to sanitation workers and anyone else who comes in contact with landfills and waste management processes. Some syringes will undoubtedly be disposed of or handled improperly prior to disposal, increasing the chance of injury. Despite their utility, conventional syringes thus clearly pose a danger to healthcare practitioners.
The prior art discloses methods of reducing or eliminating the dangers associated with exposed syringe needles. U.S. Pat. No. 4,908,022 describes a disposable safety syringe having a retractable needle. U.S. Pat. No. 5,885,257 describes a syringe having a spring-loaded, automatically retractable needle. U.S. Pat. No. 5,000,736 describes a syringe having a sealed tubular plunger from which air has been evacuated and a needle releasably attached to the distal end. After the patient is injected, the plunger seal is ruptured and the differential pressure between the vacuum and ambient air causes the needle to retract safely within the syringe body. U.S. Pat. No. 6,193,695 describes a syringe having a sealed portion between the plunger and end cap. As the plunger is pulled away from the needle to fill the syringe, a one-way valve in the sealed portion opens, allowing air to be expelled from the sealed portion. During injection, the plunger is moved toward the needle to expel its contents, the valve closes, and the pressure in the sealed portion decreases. At the end of its stroke, the plunger captures the needle, and the relatively low pressure in the sealed portion causes the plunger and needle to retract into the syringe body. Other patents of interest include U.S. Pat. Nos. 4,425,120; 4,643,200; 4,675,005; 4,692,156; 4,747,830; 4,816,022; and 4,790,822.
Although the prior art has addressed many of the safety problems related to conventional hypodermic syringes, numerous shortcomings remain relating to the cost of manufacturing and the safe use of syringes with retractable needles (safety syringes). Some safety syringes require storage of potential energy, which may be unreliable. For example, sealed vacuum chambers are prone to leakage when the syringe is stored for an extended period. Other safety syringes may have needles which retract a limited distance, with the retracted needle remaining dangerously close to the syringe body opening. Some syringes are shipped and stored with plungers fully extended, increasing their packaged size with a corresponding decrease in the efficiency of shipping and storage. Syringes which utilize springs are costly, and require additional seals to prevent contamination of the fluid drawn into the body of the syringe. Further shortcomings exist in the prior art with regard to manufacturing cost, ease of use, and reliability of safety syringes. A reliable syringe which automatically retracts the needle into the syringe body is sought which overcomes the disadvantages of the prior art.
The present invention surpasses the prior art, offering an improved safety syringe that is both reliable and economical. The retractable-needle or safety syringe of the present invention is relatively simple and convenient to operate.